1. Field of the Invention
The present invention relates to the control of a composite bridge for rectifying an a.c. power supply, for example, the mains a.c. voltage, in the vicinity of its transition through zero.
2. Discussion of the Related Art
An example application of such a composite bridge relates to the field of power converters which are meant to supply rectified d.c. power supplies, obtained from an a.c. voltage, and meant to be used as a basis, for example, for a switch-mode power supply system. The bridge is then often associated with a circuit for limiting the current surge of a storage capacitor upon power-on of a rectifier.
Another example application relates to circuits for supplying a resistive load, for example an electric radiator, which is to be supplied by a rectified a.c. voltage. The electric standard generally imposed for the power-on of such a load is in the vicinity of zero voltage of the a.c. power supply.
The conventional circuits for controlling a composite bridge have generally to be fed by a d.c. voltage with a low level with respect to the a.c. voltage. Thus, specific means are usually necessary for providing a supply voltage to the control circuit, with an insulation transformer associated to the supply means. These circuits are therefore complex and expensive.